Rotating machinery with three-phase armature windings and first and second parallel windings

ABSTRACT

Rotating machinery includes a two-pole rotor, a stator core with seventy-two slots, and three-phase armature windings, as an example. The armature winding has two phase belts per phase. The phase belt includes a first parallel winding and a second parallel winding which are arranged in the stator slots as top coils and bottom coils. When a circumferential mean position of all top coils and bottom coils included in the phase belt is defined as a phase belt center, an arrangement of the first and second parallel windings in the phase belt, as viewed in order of proximity to the phase belt center, is such that the first and second parallel windings are arranged in order of second/first/second/first/first/second/first/second/first/second/second/first parallel windings as the top coils, and the first and second parallel windings are arranged in order of first/second/second/first/second/first/first/second/first/second/second/first parallel windings as the bottom coils connected to the top coils.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent applicationserial no. 2018-159173, filed on Aug. 28, 2018, the content of which ishereby incorporated by reference into this application.

TECHNICAL FIELD

The present invention relates to rotating machinery and concerns arotating machinery that is advantageously suited for large rotatingmachinery such as e.g. turbine generators.

BACKGROUND ART

Since an output current of a large-capacity generator is large,electro-magnetic force and heat generated by armature windings arelarge. As countermeasures against this, a method is used that configuresarmature windings to form plural parallel circuits, thereby reducingcurrent per armature winding and mitigating electro-magnetic force andtemperature rise.

However, in a case where the number of parallel circuits is not adivisor of the number of poles, currents flowing through the parallelcircuits are biased and a current that circulates across the parallelcircuits arises. Due to this circulating current, loss of armaturewindings increases and coil temperature rises; this poses problems asfollows: a decrease in efficiency and a possibility of damaging to coilinsulation.

Here, first, an explanation is provided about a principle in which acirculating current across circuits is produced by increasing the numberof parallel circuits through comparison between a coil connection methodin two-pole two parallel circuits which are mainly used in largerotating machinery and a coil connection method in two-pole fourparallel circuits in which the number of parallel circuits has increasedto four.

FIG. 1 depicts a cross section of a stator of a generator. For thegenerator depicted in this drawing, when the number of poles of a rotor100 is assumed to be two, the number of stator slots 50 is seventy-twoand, therefore, the number of stator slots 50 per phase and per pole istwelve.

As depicted in FIG. 1, a stator core 10 made of magnetic steel sheetshas axially elongated stator slots 50 formed along its innercircumference at predetermined intervals in a circumferential directionto hold armature windings therein and there are teeth 40 between each ofthese stator slots 50 in the circumferential direction. Two armaturewindings are held inside each of the stator slots 50 at top and bottom(inner and outer circumference sides) in a radial direction; a coil heldin an inner circumference side is referred to as a top coil 20 and acoil held in an outer circumference side is referred to as a bottom coil30.

FIG. 2 is a diagram of the circumferentially developed stator depictedin FIG. 1, where U phase armature windings are depicted out of armaturewindings of three phases U, V, and W. Also, a coordinate axis θindicates a circumferential direction and a coordinate axis Z indicatesan axial direction. The coordinate axes in FIGS. 1 and 2 indicate thesame directions.

As depicted in this drawing, top coils 20 and bottom coils 30 are heldin the stator core 10, positioned at regular intervals in thecircumferential direction. Since the number of stator slots 50 per phaseand per pole is twelve, there are twelve top coils 20 and twelve bottomcoils 30 for each pole, i.e., twenty-four coils for each of two poles.Here a coil Group of top coils 20 and bottom coils 30 that arepositioned for one pole is defined as a phase belt. This phase belt is acoil group which is denoted by a reference numeral 60 in FIG. 2. Areference numeral 70 denotes a terminal.

Here, U1 and U2 are taken to denote two parallel circuits. In the caseof two-pole two parallel circuits, by configuring one phase belt 60 asU1 and the other phase belt 60 as U2, currents flowing through theparallel circuits are balanced and no circulating current across theparallel circuits arises. However, in a case where the number ofparallel circuits is increased to four for the sake of currentreduction, it is needed to allocate two parallel circuits U1 and U2 toone phase belt 60. In that case, currents flowing through U1 and U2 arenot balanced and a circulating current across the parallel circuitsarises.

One method for restraining the circulating current is to changecombinations of coil connections. For example, Japanese UnexaminedPatent Application Publication No. 2015-91205 (Patent document 1)describes a connection method for reducing the number of jumperconnections, so that the circulating current across circuits will berestrained even in an arrangement of two-pole four parallel circuits inwhich armature windings are configured; this is depicted in FIG. 3. FIG.3 only depicts one phase belt and the other phase belt is the same.

According to Japanese Unexamined Patent Application Publication No.2015-91205 (Patent document 1) depicted in FIG. 3, in the arrangement oftwo-pole four parallel circuits in which armature windings areconfigured, the number of jumper connections 80 is reduced, so that thecirculating current across circuits will be restrained even in sucharrangement. In this arrangement, top coils 20 and bottom coils 30 areheld inside stator slots (see FIG. 1), placed in inner and outerpositions respectively inside the slots. The top coils 20 and bottomcoils 30 are connected to form armature windings. The armature windingsare grouped in 2n phase belts 60 per phase and each of the phase belts60 is comprised of pairs of parallel windings. When a circumferentialmean position of all top coils 20 and bottom coils 30 included in eachof the phase belts 60 is defined as a phase belt center and anarrangement of first and second parallel windings in at least one phasebelt 60 is viewed in an order of proximity to the phase belt center, thefirst and second parallel windings are arranged in an order of thefirst, second, second, first, first, second, first, second, second,first, second, and first parallel windings in the top coils 20 or thebottom coils 30, and the first and second parallel windings are arrangedin an order of the first, second, second, first, second, first, first,second, first, second, second, and first parallel windings in the otherbottom coils 30 connected to the abovementioned top coils 20 or theother top coils 20 connected to the abovementioned bottom coils 30.

SUMMARY OF THE INVENTION

However, according to study of the inventors, in the technical approachdescribed in Japanese Unexamined Patent Application Publication No.2015-91205 mentioned above, the number of jumper connections 80 isreduced, but the circulating current in load operation may not decreaseso much, and it is deemed likely that this approach does not lead toreduction of loss.

An object of the present invention which has been developed in view ofthe point noted above is to provide a rotating machinery in which thecirculating current in load operation can be decreased and loss ofarmature windings can be reduced.

In order to achieve the foregoing object, a rotating machinery of thepresent invention includes a 2n-pole rotor, a stator core with 72nstator slots, and three-phase armature windings, where n denotes aninteger not less than 1. Each of the stator slots houses a top coil onan inner radius side of each of the stator slots and a bottom coil on anouter radius side thereof. Each of the armature windings is formed byconnecting the top coil and the bottom coil and has 2n phase belts perphase. Each of the phase belts includes a first parallel winding and asecond parallel winding. The first and second parallel windings arearranged in the stator slots as the top coil and the bottom coil.Assuming that a circumferential mean position of all top coils andbottom coils included in each of the phase belts is defined as a phasebelt center, an arrangement of the first and second parallel windings inat least one phase belt, as viewed in an order of proximity to the phasebelt center, is such that the first and second parallel windings arearranged in an order of the second, first, second, first, first, second,first, second, first, second, second, and first parallel windings as thetop coils or the bottom coils, and the first and second parallelwindings are arranged in an order of the first, second, second, first,second, first, first, second, first, second, second, and first parallelwindings as the other bottom coils connected to the abovementioned topcoils or the other top coils connected to the abovementioned bottomcoils.

According to the present invention, the circulating current in loadoperation can be decreased and loss of armature windings can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a stator of a rotating machinery;

FIG. 2 is a connection diagram in which the stator of the rotatingmachinery illustrated in FIG. 1 has been developed circumferentially,depicting only U phase armature windings and terminals in an arrangementof two-pole two parallel circuits;

FIG. 3 is a diagram depicting a method of connections in a phase beltwith regard to a rotating machinery of prior art (Patent document 1);

FIG. 4 is a diagram depicting a method of connections in one phase beltwith regard to a first embodiment of a rotating machinery of the presentinvention; and

FIG. 5 is a diagram representing a ratio between coil current and loadcurrent under a rated load condition with regard to the presentinvention and prior art (Patent document 1).

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, a rotating machinery of the present invention isdescribed based on an embodiment illustrated. Now, identical referencenumerals are used to denote components corresponding to those in FIGS. 2and 3.

FIG. 4 depicts a method of connections in one phase belt with regard toa first embodiment of a rotating machinery of the present invention.

As depicted in this drawing, the rotating machinery of the presentembodiment includes a rotor with 2n poles, when n is assumed to be aninteger of 1 or more, a stator with 72n stator slots 50, and armaturewindings of three phases, with top coils 20 and bottom coils 30 beingheld inside the stator slots 50, placed in inner and outer positionsrespectively inside the slots. The top coils 20 and the bottom coils 30are connected to form the armature windings. The armature windings aregrouped in 2n phase belts 60 per phase and each of the phase belts 60includes pairs of parallel windings. Assuming that a circumferentialmean position of all top coils 20 and bottom coils 30 included in eachof the phase belts 60 is defined as a Phase belt center 60 a, anarrangement of the first and second parallel windings in each pair in atleast one phase belt 60, as viewed in an order of vicinity to the phasebelt center 60 a, is such that the first and second parallel windingsare arranged in an order of the second, first, second, first, first,second, first, second, first, second, second, and first parallelwindings as the top coils 20, and the first and second parallel windingsare arranged in an order of the first, second, second, first, second,first, first, second, first, second, second, and first parallel windingsas the bottom coils 30 connected to the top coils 20.

The configuration according to the present embodiment as above can makethe circulating current in load operation smaller than in related artand can provide a rotating machinery equipped with armature windingswith reduced loss.

FIG. 5 represents a ratio between coil current and load current under arated load condition with regard to the present invention and prior art(Patent document 1).

As is obvious in this drawing, a maximum value of the coil current/loadcurrent ratio for the present invention is 100.2% and a minimum valuethereof is 99.9%. A difference between these values is smaller than thedifference between a maximum value of 101.5% and a minimum value of 98.7of the coil current/load current ratio for the prior art (Patentdocument 1).

A smaller difference (smaller unbalance) between the maximum and minimumvalues of this coil current/load current ratio indicates a smallercirculating current. Therefore, it can be said that the presentinvention can make the circulating current smaller than in prior art(Patent document 1).

Now, the embodiment works equally well even in a case where thecombinations of the top coils 20 and the bottom coils 30 are inverted inthe connections described previously for the first embodiment. Similareffectiveness can be obtained, for example, even in an arrangement inwhich the bottom coils 30 are arranged, from the center of the phasebelt 60, in a sequence of second, first, second, first, first, second,first, second, first, second, second, and first parallel windings andthe top coils 20 connected to the bottom coils 30 are arranged in asequence of first, second, second, first, second, first, first, second,first, second, second, and first parallel windings.

In addition, while the method of connections according to the firstembodiment is used to configure windings in a rotating machinery havingan arrangement of four parallel circuits with two poles and seventy-twoslots, it goes without saying that the first embodiment is applicablefor a rotating machinery having an arrangement of 4n parallel circuitswith 2n poles and 72n slots, when n is assumed to be an integer of 1 ormore, because the number of slots per phase and per pole is twelve evenin the latter rotating machinery.

Now, the present invention is not limited to the described embodimentand various modifications are included therein. For example, theforegoing embodiment is one described in detail to explain the presentinvention clearly and the invention is not necessarily limited to thatincluding all components described. A subset of the components of anembodiment can be replaced by components of another embodiment. To thecomponents of an embodiment, components of another embodiment can beadded. For a subset of the components of each embodiment, othercomponents can be added to the subset or the subset can be removed orreplaced by other components.

REFERENCE SIGNS LIST

10 . . . stator core, 20 . . . top coil, 30 . . . bottom coil, 40 . . .teeth, 50 . . . stator slot, 60 . . . phase belt, 60 a . . . phase beltcenter, 70 . . . terminal, 80 . . . jumper connection and 100 . . .rotor.

What is claimed is:
 1. Rotating machinery comprising a 2n-pole rotor, a stator core with 72n stator slots, and three-phase armature windings, where n denotes an integer not less than 1, wherein: each of the stator slots houses a top coil on an inner radius side of each of the stator slots and a bottom coil on an outer radius side thereof; each of the armature windings is formed by connecting the top coil and the bottom coil and has 2n phase belts per phase; and each of the phase belts includes a first parallel winding and a second parallel winding, wherein the first and second parallel windings are arranged in the stator slots as the top coil and the bottom coil, and assuming that a circumferential mean position of all top coils and bottom coils included in each of the phase belts is defined as a phase belt center, an arrangement of the first and second parallel windings in at least one phase belt, as viewed in an order of proximity to the phase belt center, is such that the first and second parallel windings are arranged in an order of the second, first, second, first, first, second, first, second, first, second, second, and first parallel windings as the top coils or the bottom coils, and the first and second parallel windings are arranged in an order of the first, second, second, first, second, first, first, second, first, second, second, and first parallel windings as the other bottom coils connected to the abovementioned top coils or the other top coils connected to the abovementioned bottom coils. 